Electronic computer



EXAMINER rr. kDu. .N rr. m EL Dn, S S 0 Dn c.

Feb. 4, 1947. J. A. RAJCHMAN yELICI'ROHI() CDIPUTER F1194 April'so. 1942 Sheets-Stalen 2 UNITED STATES PATENT OFFICE ELECTRONIC COMPUTER Jan A. Rajchman, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application April 30, 1942, Serial No. 441,170

8 Claims. (Cl. 23S-61) 2 the drawings, of which Fig. 1 is a schematic diagram of a preferred embodiment of the invention; Fig. 2 is a schematic circuit diagram of the principal electrical circuits; and Figs. 3, 4 and 5 This invention relates generally to computing devices and particularly to electronic computers in which a function of two variables is continuously indicated in terms of an electric current or voltage. 5 are elevational views of the variable density Heretofore, various electronic computers have screens which are components of the system of been known which utilized moving mechanical Fig. 1. parts for light scanning either predetermined Referring to Fig. 1, the horizontal deflection ducial marks or apertures formed by adjustable elements 6 of the cathode ray oscillograph tube mechanical elements. This invention is a modi- 10 8 are supplied with deflecting voltages from a cation of the method and apparatus described rst variable D.C. source I, the output voltage by applicant in his copending application, Serial of which is proportional to the value of the first No, 441,169, led April 30, 1942, Both of these variable X. The vertical deflection elements 1 of applications contemplate the elimination of al1 the cathode ray oscillceraph tube 8 are supplied moving mechanical elements in the computer per with deiiecting voltages from a second D.C. se, and utilize the substantially inertialess movesource 2, the output voltage of which is proporment of a cathode ray beam for scanning in any tional to the value of the second variable Y. The desired manner a screen of predetermined variavariable D.C. voltages in the SOUICSS l and 2 may ble density. It will be clear that the accuracy of be obtained from a, battery and potentiometer, the device is determined principally by the line- 'the sliding COIltaCt 0f Which iS actuated by the arity with which the cathode ray beam may be device under observation, cr in any other well deected in response to deecting voltages which kIlOWn mannel- Il? Will be apparent that the are a function of the variables under consideracathode ray in the oscillograph tube 8 will be detion, and the accuracy of the predetermined varilected predetermined distances along the Vertiiation of the screen density. cal and horizontal axes which are substantially An object of the invention is t0 provide en 1mproportional to the values of the variables Y and proved method of and means for computing elec- X, respectively. The cathode ray beam will. in tronically a predetermined function of two varia Well kDOWD manner. PlOdllCe an illuminated ables, Another object is to provide an improved spot on the uorescent screen 54 of the cathode method of and means for computing electroni- 3o ray tube 8. The light spot on the iluorescent cally, without the use of moving mechanical ele- Screen 54 iS fOCIlSed by the lens System 55 011 a ments, a function of two variables expressed in half-Silvered mirror 9, disposed at an angle 0f terms of voltages applied to a cathode ray tube, approximately 45 degrees to the optical axis of to derive an electric current proportional in amthe lens 56. A Second half-silvered mirror IB is plitude to the desired function. Another object disposed on the same axis normal to the first mirof the invention is to provide an improved meth.. 101 9, and a third half-silvered mirror Il is 10- od of and means for continuously. deriving eleccated on the axis normal to the second mirror tronically a current which is f predetermined I0. A portion of the light image from the fluoresfunction of two variables applied to the computer cent screen 54 is transmitted through all three interms of voltages proportional to the instantamirrors and applied to the variable density neous value of each variable. Still another object screen I2 (see Fig. 5), the density of which varis to provide an improved method of and means ies in a predetermined manner, with the radius for correcting errors in such an electronic comfrom the point 0 which corresponds to the posi puter caused by non-linearity of the component tion of the light beam when the variables X and electronic elements. 1 y 45 Y are both of zero value. The light transmitted 'I'his invention diiiers from applicants above by the screen I2 is focused by the lens I3 upon the mentioned copending application in that instead diffusion screen I I. A light responsive device I5, of scanning predetermined ilducial marks on which may be an electron multiplier of the RCA transparent screens, the present method comtype 931, located in light responsive relation with prises deflecting the light image of a cathode ray respect to the diiusion screen I l, generates a across screens of variable density to derive from voltage proportional to the received l'ght intenssuitable light responsive devices voltages proporu tional to the light intensity transmitted through ampliiler I6 having a feedback stabilization cirthe' screens. cuit II described hereinafter. The output of the The invention will bedescribed by referenceto Q5 amplifier .I6 is applied to the resc'mer I8, the

ity. 'I'his voltage is ampliied by the conventional D.C. output of which is passed by the 25 kc. rejection filter I9 to a suitably calibrated indicator 20. Readings on the indicator 20 are proportional to the desired function of X and Y. In order to overcome errors caused by the dark currents in the photosensitive electron amplifier I5, the cathode ray is modulated by applying the output of a 25 kc. oscillator 3 to one of the cathode ray oscillograph control grids 4. Readings on the indicator 20 are proportional to the amplitude of the 25 kc. voltages in the circuit and independent of the D.C. component in the electron multiplier output.

The low intensity of the spot produced on the fluorescent screen 54 is normally subject to considerable variation due to non-uniformity of the fiuorescent screen, internal charging effects, and the angle of incidence of the light beam with the lens 56. A portion of the light applied to the rst half-silvered mirror 9 is reected to the lens 43 and focused upon the diffusion screen 44. A second light sensitive electron multiplier 45, which may also be of the RCA type 931, located in light responsive relation with respect to the diffusion screen 44, produces a voltage which is substantially proportional to the light transmitted by the lens system 56. This voltage is applied to the input of a conventional amplifier 46 including a feedback stabilization circuit 41. The output of the amplifier 46 is applied to the rectier 48. The D.C. voltage thus derived is subtracted from a D.C. standard voltage 50, which may be a battery source, and is applied to the input of a second D.C. amplifier 5I through the 25 kc. rejection filter 49. The output of the D.C. amplifier I is connected to the control grid 4 of the cathode ray oscillograph tube 8 to apply potentials which correct for variations in the light intensity of the spot on the uorescent screen 54.

The arrangement described has been found to stabilize the light intensity transmitted by the lens system 56, to one part in 50 for a moving light spot and to one part in 100 for a stationary light Spot.

In order to correct for non-linearity in the deiiection of the cathode ray beam with respect to the deflecting voltages applied to the horizontal and vertical defiection elements, a portion of the light applied to the second half-silvered mirror I0 is reflected to the variable density screen 22, the density of which varies linearly in a vertical direction, and a portion of the light applied to the half-silvered mirror I I is reected to the variable density screen 32, the density of which varies linearly in a horizontal direction. The details of these screens are illustrated in Figs. 3 and 4. The light transmitted by the screen 22 is focused by the lens 23 on a diffusion screen 24. A photosensitive electron multiplier which may be of the RCA 931 type, located in light responsive relation with respect to the screen 24, generates voltage proportional to the intensity of the light transmitted by the screen 22. This voltage is applied to the input of a conventional amplifier 26 which includes a feedback stabilizing circuit 21 described hereinafter. The output of the amplifier 26 is applied t-o the rectifier 28. The output of the rectifier 28 is applied, through the 25 kc. rejection filter 29, to the input of the conventional D.C. amplifier 30, where it is subtracted from the voltage derived from the D.C. source 2. The output of the amplifier 30 is connected to the vertical deflection elements 1. It will be apparent that the vertical deflection of the cathode ray tionally to the intensity of the light beam transmitted by the variable density screen 22. Therefore, D.C. voltages derived from the output of the lter circuit 29 may be applied to the vertical deflection D.C. amplifier 30 to correct for nonlinearity in vertical deflection.

Similarly, the light transmitted by the variable density screen 32 is focused by the lens 33 upon the diffusion screen 34. Voltages derived from the light sensitive electron multiplier 35, located in light responsive relation with respect to the diffusion screen 34, are applied to the input of the conventional amplifier 36 which includes a feedback stabilization circuit 31. The output of the D.C. amplifier 36 is applied to the input of the rectifier 38. The output of the rectifier 38 is connected through the 25 kc. rejection filter 29 to the horizontal deflection D.C. amplifier 40 and subtracted from the voltage derived from the D.C. source I, to correct for non-linearity in horizontal deflection. The output of the D.C. am-

plifier 40 is connected to the horizontal deection.

elements 6.

Figure 2 includes the cathode ray oscillograph tube 8, the light responsive device I5, the amplier I6 with stabilization circuit I1, the rectifier I8 and the 25 kc. rejection filter I9 for deriving currents for actuation of the indicator 2U. The light responsive device 45, the amplifier 46 with its stabilization circuit 41, the rectifier 48, the source of standard voltage 50, the 25 kilocycle rejection filter 49 and the D.C. amplifier 5I are connected to the electron beam control grid 4 to compensate for variations in the intensity of the light beam emitted from the fluorescent screen 54 of the cathode ray tube 8. The light responsive devices and circuits for compensating for non-linearity in the vertical and horizontal deflection of the cathode ray beam are omitted for the sake of simplicity since they correspond in all respects to the circuit described for the lndication of the desired function of the two variables X and Y.

The light responsive electron multiplier I5 is supplied with suitable positive potentials from selected points on the voltage divider 66. The voltage regulator .6I which may be of the RCA V12-150, or similar, type is provided for stabilizing the potentials in this circuit. The output of the light responsive device I5 contains both D.C. and 25 kc. components. The 25 kc. component is applied to the input of the first amplifier tube 1 I, the output of which is coupled through a conventional resistance-capacity network to the input of the second amplifier tube 12. A stabilization feedback circuit I1 comprising a resistancecapacity network couples the anode of the second amplifier tube 12 to one of the grid electrodes of the first amplier tube 1 I. The amplified 25 kilocycle signal derived from the second amplifier tube 12 is applied to a rectifier circuit I8. The D.C. component of the demodulated signal is passed by the 25 kc. rejection filter I9 and applied to the indicator 20 which is calibrated in terms of the desired function of X and Y.

A portion of the light impinging on the halfsilvered mirror 9 is refiected to the light sensitive electron multiplier 45. The multiplier is supplied with suitable operating voltages from selected points on the voltage divider 65. The 25 kilocycle component of the multiplier output is amplified in the 2 stage amplifier circuit 46, stabilized by the feedback circuit 41, and demodulated by the rectifier 48 in the same manner as described beam will produce voltage which varies propor- 73 heretofore'for the circuits 16, I1 and I8. The

D.C. output component of the rectiner 4B is subtracted from a standard D.C. voltage source 50, which may include a battery and potentiometer, and applied to the input of the 2 stage D.C. amplier circuit 5I through the 25 kilocycle rejection lter 49. The D.C. output signal of the ampliiier 5I is further stabilized by the conventional voltage regulator tubes 62, 63 and 64 which may be of the RCA X7R-150, or similar, type The output of the amplifier 5I, or the stabilized output derived from the voltage regulator circuit, is selected by the switch 13, and applied with the 25 kc. modulating signal, to the control grid l of the cathode ray oscillograph tube 8, to compensate for variations in the intensity of the luminous spot on the uorescent screen 54. Suitable voltage dividers may, if desired, be provided for biasing the beam deflection to adjust for desired zero values of the variables X and Y.

II a plurality of different functions of the variables X and Y are to be indicated simultaneously, the light transmitted by the third half-silvered mirror l I (see Fig. 1) may be divided into as many light responsive electron multipliers as desired. This light may illuminate lters, the density of which vary, in any desired manner, from .a common point representing the zero value of the variables. The output of the additional multipliers, one of which 55 is shown by dash lines in Figure 1, with its associated' circuits, are applied to suitably calibrated indicators.

Figure 3 indicates the variation in density of the screen 32 for correction of non-linearity in horizontal deection of the electron beam. Figure 4 indicates the variation in density of the screen 22 for correction of non-linearity in vertical deection of the electron beam. Figure 5 illustrates the variation in density of the screen I2 which transmits the portion oi the light beam from which is derived the desired function of the variables X and Y. If the variation in density is linear radially from the point 0 the indicated function will be a diagonal of a rectangle formed by the variables X and Y. By suitably varying the density gradation, other desired functions may be readily obtained.

The screens should be prepared by etching or photographic means to. as accurately as possible, provide the desired density gradation. One wellknown method of preparing such screens is to photographically reduce to the desired size a large drawing or half-tone picture.

I claim as my invention:

1. An electronic computer for deriving a predetermined function of two independent variables including a cathode ray tube having ray generating meansjray deecting means and a fluorescent screen in the path oi said ray. means for determining the horizontal deection of said ray by the instantaneous value of one of said variables, means for determining the vertical deflection o! said ray by the instantaneous value of the other of said variables, a second screen of vari able density, means for forming an image of said nuorescent screen on said second screen, means for deriving voltages proportional to the inten-- sity of the light transmitted by said second screen,. and means for indicating the amplitude of said voltages.

2. Apparatus of the type described in claim l including means for maintaining substantially constant the average light intensity applied to said second screen.

3. Apparatus of the type described in claim 1 including means for compensating for non-1inearity in the deilection of said ray with respect to the voltages representing said variables.

4. Apparatus of the type described in claim 1 including means for diverting a portion of the light from said fluorescent screen, means for deriving from said diverted light voltages proportional to the vertical and horizontal components of said ray deection, and means for utilizing said voltages to compensate for non-linearity in the deflection o! said ray.

5. Apparatus of the type described in claim 1 including means for diverting a portion of the light from said iluorescent screen, means for deriving from said diverted light voltages proportional to the intensity of said light, and means for utilizing said voltages to compensate for variations in the intensity of said light.

6. Apparatus of the type described in claim 1 including means :for diverting a portion of the iight from said fluorescent screen, means for deriving from said diverted light voltages proportional to the intensity of said light, means including a light responsive device and at least one variable density screen for deriving from said diverted light voltages proportional to non-linearity in the vertical and horizontal components of said ray deflection, and means for utilizing said voltages to compensate for said variations in the deflection of said ray.

7. Apparatus of the type described in claim 1 including means for diverting a portion of the light from said iluorescent screen, means for deriving from said diverted light voltages proportional to the intensity of said light, means including a light responsive device and a source of standard voltage for deriving from said diverted light voltages proportional to variations in the intensity of said light, and means for utilizing said voltages to compensate for variations in said light intensity.

8. Apparatus of the type described in claim 1 including means for modulating the intensity of said cathode ray for deriving a control potential for maintaining substantially constant the average light intensity derived from said fluorescent screen.

JAN A. RAJCHNLAN. 

